1. Field of the Invention
The invention lies in the domain of operable packaging of data recording devices and means. More particularly the invention relates to optical tape recording cartridges.
2. Description of the Prior Art
Tape recording and reading of data and, of course, operable packaging thereof for convenience of recording, playing, promoting and distributing the same have been around for some time to include punched paper tape, magnetic tape, being readable by magnetic means; and, more recently, optically recordable tape with both RAM (erasable) and ROM applications, being readable by optical means. Indeed, numerous magnetic tape cartridges, cassettes and video tape cartridges, and even floppy disc and optical disc envelopes have been designed with convenience of use and application in mind as well as for protection of the tape or disc and data thereon.
In all prior tape applications, however, it was necessary that the tape physically pass over or be wrapped around a read/write head. One such version caused magnetic tape to be vacuum sucked into curved contact with a concave receptacle. A rapidly spinning, circular read/write head array in quadrature, of same radius of curvature as the concave receptacle, would then write/read data across the tape width in a direction almost orthogonal to direction of travel of the tape. In effect the tape was wrapped around a portion of the periphery of a read/write head array. Subsequently, it was found that more data could be recorded by increasing the angle of the recording path from the orthogonal; i.e., this was acomplished by changing the angle of the write/read head from the nearly transverse to a very much reduced angle more parallel, logitudinally to the direction of tape travel, as practiced by AMPEX.
Subsequent to the AMPEX concept, a Sony "U-matic" tape recording concept emerged, wherein the tape was physically passed nominally 180.degree. around a circular head, i.e. in the shape of a "U." Again, in all of the prior tape applications, direct physical contact with an optical head was necessary.
However, with the advent of optical tape, as an off-shoot of the original and widely distributed video disk, the requirement that the tape be flexible required that it be a first-surface recordable medium rather than the second-surface recordable medium inherent in said video disk. As a first-surface recordable medium, optional tape is subject to foreign matter and particulate contamination on the surface thereof as well as potential damage by physical contact to the relatively fragile tape laminates and alteration or destruction of data thereon. Such problems either did not exist or were nominal with respect to video disks.
An optically recordable WORM (write once read many times) video disk usually consists of a relatively inflexible, premolded polymethylmethacrylate (PMMA), polycarbonate or polyolefin substrate with either spiral or concentric grooves embossed thereon, to which is superimposed, in one version, a very thin metallic or reflective layer, then a very thin dye polymer, photoreactive layer, and finally a relatively thick transparent protective coating. While the disk is spun, data bits are recorded in said spiral or concentric paths and read by light beam means in an optical head having a coarse path-tracking adjustment by radial movement of said head across and immediately above the surface of said disk, and a fine adjustment in the form of a galvano mirror and a voice coil operated objective lens combination to reflect and focus said beam to a spot on a recordable or recorded path. Since said path is spirally or concentrically spaced per turn of the disk at a pitch of about one and one-half micrometers (1.5 um), while the path is about a half micrometer (0.5 um) in diameter, typical dust particles being in the realm of a micrometer (1.0 um) or so in size lying on the recordable dye polymer laminate could obscure or completely eclipse data if it were not for the fact that the protective layer of a typical optical disk is in the realm of a millimeter (mm) or 10.sup.3 um in thickness. Dust particles on the surface of a typical optical disk lie approximately 1.0 mm from the dye polymer (photo reactive) laminate. A typical converging write/read light beam has a relatively high numerical aperture (NA), in the order of NA=0.5 or more, resulting in a solid cone, the apex of which is on the photosensitive dye polymer surface, the cone being truncated from the optical disk air-substrate interface. The area so intercepted by the beam at said interface is nominally 1.05 mm.sup.2 or over 10.sup.6 um.sup.2. With this understanding, it may be seen that several dust particles in the micrometer realm may be tolerated at any given spot on a functioning optical disk without affecting reading or recording of the photoreactive laminate there below.
Optical tape, on the other hand, is conventionally made of a relatively thin and flexible laminate of polyethylene terephthalate (PET) or the like, superimposed with a very thin subbing layer to smooth out the PET surface, to which is added a vacuum deposited layer of aluminum, then a dye polymer, photoreactive layer, and finally a thin anti-abrasion coating. All laminates together total approximastely 25 um. Since the anti-abrasion layer of optical tape is much thinner, in the order of a few micrometers, than the protective layer of the optical disk, in the order of 10.sup.3 micrometers, it should be readily apparent that dust particles of a micrometer or so in size, lying on the tape surface and merely a few micrometers distant from the optically active laminate, occlude significant data to be recorded, or data already recorded thereupon.
In addition, although prior art magnetic tape applications utilized conventional capstan and pinch roller means to propel and regulate speed of magnetic tape by direct physical contact with the tape surface, such means is highly undesirable if not impossible with optical tape. The necessarily very thin anti-abrasive coating of optical tape cannot be subjected to normal wear and tear of physical contact with a moving surface. And, of course, the slightest abrasion or scratching of the surface of optical tape can and will cause undesired, reflections, defractions, refractions, dispersion or diffusion of a laser beam.
Therefore, there exists a need for a tape cartridge or cassette possessing the convenience and utility of typical magnetic tape cassettes or cartridges, yet having means adapted to the unique characteristics and needs of optical tape; i.e. elimination of any possibility of particle contamination and any direct physical contact with tape recording surfaces, and providing necessary focussing, tracking and aligning characteristics inherent to optical recording media.
By providing alternate means for tape propulsion and speed control, by implementing unique focus, alignment and tracking means, and by providing a environmentally sealed cartridge design, the invention disclosed herein offers novel solutions to existing problems of broad utilization and commercial application of most optical tape recording media.